Recent studies using national data have reported that developmental disabilities are prevalent (as high as 1 in every 6 children) and on the rise in the US and elsewhere. While the cause(s) of these trends are unknown, there is concern for the potential role of exposures to environmental neurotoxicants. There is growing animal evidence that agents to which many or most people are exposed at varying levels, including contemporary-use pesticides, heavy metals, and secondhand tobacco smoke (STS), are neurotoxic. With the exception of lead, human studies of these agents in relation to neurodevelopment are lacking, both alone and together as mixtures. In many settings elevated exposure to these agents may be accompanied by nutritional deficiencies, with iron deficiency (ID) being the most common. This may result in greater neurotoxicity by acting through similar mechanistic pathways or increasing susceptibility to exposure. Pregnancy and infancy are the periods of greatest concern due to vulnerability of the developing brain. The proposed study aims to: 1) Investigate the association between neurodevelopment and early life exposure to pesticides, metals (manganese and lead), and STS individually and in combination (i.e., additive and multiplicative effects); 2) Test for interactions between these agents and ID on neurodevelopmental outcomes; and 3) Determine whether iron supplementation in pregnancy and/or in infancy ameliorates adverse impacts of environmental exposures on neurodevelopment outcome. The study will leverage two large ongoing NIH-supported studies of ID and neurodevelopment (n ~ 2500) taking place in rural China where elevated exposures, as well as widespread ID, have been documented. The study will utilize state-of-the-art approaches to assess exposures and outcomes. Detailed measures of sensory, motor, cognitive, affective-social and regulatory functions at birth/6 weeks, 9 months, and 18 months of age are collected in the ongoing studies. Exposure biomarkers will be measured in urine and blood samples from multiple time points in early development, including sensitive new methods to quantify >45 pesticides in cord blood. Expected outcomes of this study are to provide new and much needed information on the impacts of environmental exposures on neurodevelopment and prioritization of exposure risks, the specific processes and sensitive exposure windows involved the simultaneous effects of multiple exposures and ID on these endpoints, and evidence for potential interventions to lessen these effects through exposure reduction or iron supplementation. The study will likely have a significant impact on public health policy given widespread exposure to these agents worldwide, the global prevalence of ID, and increasing evidence that many environmental exposures contribute to poorer neurodevelopmental outcomes.